From e9282d4f6e303438324cab6546f532cd287d1037 Mon Sep 17 00:00:00 2001
From: Vincent St-Amour <stamourv@racket-lang.org>
Date: Wed, 25 Nov 2015 17:30:26 -0600
Subject: [PATCH] Fix `expt` of floats by large positive bignums.

Brings behavior in line with Gambit.

Closes GH #1148.
---
 .../racket-test-core/tests/racket/number.rktl |  5 +++++
 racket/src/racket/src/number.c                | 21 ++++++++++++++++---
 2 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/pkgs/racket-test-core/tests/racket/number.rktl b/pkgs/racket-test-core/tests/racket/number.rktl
index d601b473e1..0d0cb70062 100644
--- a/pkgs/racket-test-core/tests/racket/number.rktl
+++ b/pkgs/racket-test-core/tests/racket/number.rktl
@@ -568,6 +568,11 @@
 (test 0.0f0 expt -0.9999f0 (expt 2 5000))
 (test -0.0f0 expt -0.9999f0 (add1 (expt 2 5000)))
 
+(test +inf.0 expt -4.0 (expt 2 5000))
+(test -inf.0 expt -4.0 (add1 (expt 2 5000)))
+(test +inf.f expt -4.0f0 (expt 2 5000))
+(test -inf.f expt -4.0f0 (add1 (expt 2 5000)))
+
 (define (inf-non-real? x)
   (and (not (real? x))
        (= +inf.0 (abs (imag-part x)))
diff --git a/racket/src/racket/src/number.c b/racket/src/racket/src/number.c
index bb20444a58..9feb28de65 100644
--- a/racket/src/racket/src/number.c
+++ b/racket/src/racket/src/number.c
@@ -3617,18 +3617,33 @@ scheme_expt(int argc, Scheme_Object *argv[])
           }
 	}
       }
-    } else if ((d < 0.0) && (d > -1.0)) {
+    } else if (SCHEME_BIGNUMP(e) && SCHEME_BIGPOS(e)) {
       /* If `e` is a positive bignum, then the result should be zero,
          but we won't get that result if conversion produces infinity */
-      if (SCHEME_BIGNUMP(e) && SCHEME_BIGPOS(e)) {
+      double e_dbl;
 #ifdef MZ_USE_SINGLE_FLOATS
-        int sgl = !SCHEME_DBLP(n);
+      int sgl = !SCHEME_DBLP(n);
 #endif
+      if ((d < 0.0) && (d > -1.0)) {
         if (SCHEME_FALSEP(scheme_odd_p(1, &e)))
           return SELECT_EXPT_PRECISION(scheme_zerof, scheme_zerod);
         else
           return SELECT_EXPT_PRECISION(scheme_nzerof, scheme_nzerod);
       }
+      /* If d is negative, and `e` is a large enough bignum which would
+         be converted to infinity, this would return a complex NaN.
+         Instead, we want to return (positive of negative) infinity.
+         See discussion in Github issue 1148. */
+      e_dbl = scheme_bignum_to_double(e);
+      if ((d < 0.0) && MZ_IS_POS_INFINITY(e_dbl)) {
+        if (SCHEME_TRUEP(scheme_odd_p(1, &e))) {
+          return SELECT_EXPT_PRECISION(scheme_single_minus_inf_object,
+                                       scheme_minus_inf_object);
+        } else {
+          return SELECT_EXPT_PRECISION(scheme_single_inf_object,
+                                       scheme_inf_object);
+        }
+      }
     }
 
     if ((d < 0.0) && SCHEME_RATIONALP(e)) {